The invention relates to an apparatus by means of which plates input as a stack are isolated in modern processing machines for offset printing plates such as, for example, exposure machines, and wherein intermediate paper layers which are usually present are removed.
There is a desire in modern machines of the graphics trade, particularly in exposure machines for offset printing plates, to individually remove the plates from a magazine. The unexposed offset plates are normally supplied in packages of 50 to 100 articles, whereby the individual plates are protected by intermediate layers of thin paper due to their sensitive surface. Insofar as possible, the plate stack should be inserted into the magazine in the same way in which it was removed from the outer packaging. From the magazine, the plates should be individually removed, for instance by means of a suction plate or gripper, and should then be supplied for further processing.
This operation, which may seem rather simple at first, is complicated by a number of conditions in view of current practices.
The light-sensitive layer side of the plates is extremely sensitive to scratches. The plates, therefore, dare not slide on other surfaces, for instance parts of the conveyor means, or on one another in any situation.
In the condition in which they are delivered, the plates are usually separated from one another by intermediate layers of paper so that they cannot rub against one another. This intermediate paper layer, however, must be respectively removed after a plate is taken from the stack.
In the condition in which they are delivered, the plates of the stack adhere greatly to one another. In order for the uppermost plate to be reliably taken from the stack without disruption, it is necessary to first loosen it from the plate stack by means of an isolating operation.
Plates having different formats should be processed with one and the same magazine.
The lifting element should always grasp the individual plates in the same position.